Rubber compound and method of making the same



Patented a. 10, 1933 f ,929,544. c v U OO PO D AND METHOD G' THE SAME Frank 0. Woodrufi, Quincy, Mass z assignor. to

Harry H. Beckwith,qBro0kline, Mass.

" No Drawing.. Application April 9, 1930 c Serial No. 442,99 8

14 Claims. 7 (o1. 106-23) production of rubber coagulum to be used in. manufacturing rubber articles of all kinds, the.

' substitute substance or substances being such. as to yield acoagulum closely resembling in every way pure coagulated rubber and comparing iavorably in tensile strength-withpure rubber... In a other words, the'chief object of the invention is dispersion of rubbersuch as latex so as to materially; increase the quantity of. coagulated product obtained from a given amountof rubber 72 0 acteristics'of the product. I l

Latex is a term applied to, certain juices extracted from a considerable number of differenttrees, these juices in this case being capable of yieldingsome kind'of rubber. the, one of principal importance is H evea braziliensis, this yielding a latex fromwhich the well known Para rubber is derived, Latex from this tree consistsoi a natural colloidal-dispersionof rubber globules in a Watery vehicle, and containsabout 34 to 39 percent of solids depending on conditions such as seasons, age of ftree, etc. The rubber globules are believed to consist of a core ofterpena represented by the chemical symbol (051-1911 surrounded by a coating of proteid matter. The W'atery vehicle in which the rubber particles are suspended also contains proteids which apparently keep the rubber globp particles'and the diluent particles tounite in 'ule's separate. These. proteids are subject to decomposition and putrefaction, so that if it is 40 desiredto transport latex or tokeep it for more than a day or two, it is necessary to add a preservative, such as a small quantityof ammonia or formalin. Y

In preparing rubber for industrial uses, the

globules of rubber may be coagulated'in .the latex by any of a number of methods which are supposedtobreakdown or destroy the agencies in latex which tend to keep the globules separate. ;It is an object of the present invention toincreasethe yield from an aqueous dispersion. of rubber suchas latex by mixing with the dispersionother substances which will .react chemically to form a suitabledi-luent or filler for the rubber, the reactionbeing-preferably of a nature toresult in the simultaneouscoagw to use substitute materials-with an aqueous without appreciably altering the physical char- Of these trees,

lation .of the rubber "and. diluent substances in ahomogeneous mass, the physical characteristics of which closely resemble those-of pure coagulated rubber. V J I, U V

V In carrying out my invention, I preferably 80;, add to latex (taken directly fronithe tree or preservedwith ammonia) a quantity of onefor more diluent materials such as oils, gums, resins or other colloids. Theproduct obtained from properly coagulatedi mixtures of rubber :ancl; suitable diluents varies with the'kindand quan- 'tities of the diluents used. .While there are many difierent substanceswhich are capable of .beingcombined with rubber molecules ;:so as to form a rubbery, non-jsticky coagulum, it. is 9; preferable to employ diluent substances which are not themselves subject. to deterioration with age. Thus, according to'the present invention,

I preferably employ water soluble gums and 'mineral oils, neither of these classes of substances being :--su bject to deterioration by beu coming rancid or by. fermentation. Where. the" ultimate rubber products are intended for use Y over an extended period of time, the chemical stability of the diluent materials is of considerableimportanca. i

In forming a coagulumin which dispersed rubber has-been combined with a diluent substance so as .to substantially increase the quan-, tity of coagulum obtained from a given amount of rubberwithout materially changing its phy- 'sical characteristics, the ingredients must be brought together in a certain mannerin order to obtain a non-sticky, cohesive, rubbery coagulum, especially if aproduct-is desired having relatively great tensile strength after vulcanization. .In bringing together the, rubber uniformity as well as thestrength of the. ultimate product. After the dispersed rubber and diluent substances have been thoroughly mixed I preferably precipitate a combined coagulum by stirring into,the mixture a small. quantity of an aldehyde, such as formaldehyde, acetalde- -hyde, benzaldehyde or furfural. The efiect' of ently divided into two portions.

portions 3 parts of finely divided sulphur is mate product being of the same order as that i of pure vulcanized rubber.

As an example of a specific application of my method, I take fifty parts of rubber in an aqueous dispersion, such as latex, thirty. to forty parts of a water soluble gum, such as gum arabic, and twenty to ten parts of a suitable oil, preferably a mineral oil which is not subject to deterioration with age. For this purpose a refined petroleum oil is satisfactory. The gum may be dissolved in three times its weight of water, The oil 'isflpreferably emulsified as by mixing with. the gum solution and circulating the mixture through a colloid mill so that the particles become very finely divided and a stable emulsion is formed, the gum acting as an emulsifying agent; The emulsion is then mixed with the rubber dispersion by careful stirring. To this mixture I may add a small quantity of an aldehyde, formaldehyde being effective and convenient. The formaldehyde solution is preferably added slowly and stirredinto the mixture. The mixture may also be'slightly warmed during the additionof the formaldehyde. If a forty per cent solution'of formaldehyde is used, the quantity of solution of this strength sufficient to bring about a successful coagulation of the solids in the mixture will be approximate- 1y two per cent of the total weight of solids in the mixture. After the coagulation is complete, a clear watery serum separates therefrom. This serum is entirely free from particles of rubber or gum, and is also free from any trace of oil. If the serum is passed through a filter paper; no residue is left thereon.

Prior to mixing the ingredients together, vulcanizing reagents may be conveniently added thereto so that after coagulation, the coagulum.

has distributed therein suitable quantities of vulcanizing reagents. For example, in' carrying out the process as hereinbefore described in detail with 50 parts rubber in dispersed form, to partsgum arabic, and 20 to 10 parts mineral oil, the gum solution maybe conveni- To one of the added and mixed in. Then ammonia is added to the mixture. Into the other portion of gum solution 5 parts of zinc oxide may be mixed. The two portions may then be mixed together with the oil, and the whole mixture passed twice through a colloid mill. This reduces the maximum particle size for all the ingredients in the mixture to about one-half micron. The mixture is then taken from the colloid mill and cooled,

a small amount of ammonia being preferably added. After cooling, the mixtureis stirred carefully into latex or other dispersion of rubber whereupon an aldehyde is-gradually added, preferably with gentle warming, until coagulation takes place. The coagulum is washed and dried, then milled for a few minutes with A;% of a suitable accelerator, after which it can be vulcanized in the usual manner. This formula yields rubber products which are characterized by particularly high tensile strength and long If properly made, this coagulum life. By following the formula, vulcanized samples have been made having a tested tensile strength exceeding 3400 lbspper square inch. This compares favorably with the strength of the best pure rubbers which have been similarly vulcanized and tested. It is obvious that the specific proportions of ingredients given herein by Way of example may be varied, and other equivalent ingredients may be employed instead of or in addition to those mentioned without departing from the scope of the invention.

I claim:

"1. A method of preparing a rubber coagulum, which, comprises mixing with a quantity of dis- .persed rubber a quantity of diluent material capable of forming a rubbery coagulum with the rubber and including mineral oil in the form of a stable emulsion and an emulsifying agent therein, and thereafter adding a small quantity of an aldehyde to resolve the mixture into a non-sticky, resilient, rubbery. coagulum containing all the rubber anddiluent present and a clear watery serum. I i

2. A methodof' preparing a rubber coagulum, which comprises mixing with a quantity ofdis persed rubber a quantity of diluent material capable of forming a rubbery coagulum with the rubber and including an aqueous emulsion much water, adding to a portion of the gum solution 3 parts of finely divided sulphur and'a small quantity of ammonia, adding to the other portion'of gum solution 5 parts of zinc oxide, mixing together the portions of gum solution with 20 to 10 parts of oilto makeparts'of gum and oil, emulsifying the oil in the gum solution, mixing the emulsion with'latex'containing 50 parts of rubber, coagulating the solidsin the mixture by graduallystirring in -a small quantity of an aldehyde and warming, washing and drying the resulting coagulum, milling into the coagulum 4% of an accelerator, and vulcanizing the milled mass.

4. A method of preparing a rubber coagulum which comprises making a stable emulsion of mineral oil with a water-soluble gum as emulsifying agent, adding tothe emulsion a dispersion of rubber containing an amount of rubber substantially equal to the quantity of oil and solids in the emulsion, and coagulating the mixture by stirring, inasmall quantity of i an aldehyde with gentle warming.

5. A method of preparing a rubbercoagulum, which comprises dissolving a quantity of watersoluble gum, mixing the dissolved gum with a lesser quantity of mineral oil, passing themixture through a colloidmill whereby the particles of gum and oil are finely divided and a stable emulsion is formed, adding the mixture to a quantity of latex containing a weight of rubber equal to the combined weights of the gum and oil in the mixture, stirring into the mixture a small quantity of formaldehyde and warming the mixture during the addition of the formaldehyde until coagulation takes place.

6. A method of making a non-sticky, resilient, rubbery coagulu which comprises emulsifying an oil with a suflicient'quantity of an emulsifying agentto form a stable emulsion, mixing with the emulsion a quantity of dispersed rubber not less in weight than the combined weights of the oil and emulsifying agent, and coagulating the mixture by stirring in a small quantity of an aldehyde.

7.- A method of making a non-sticky, resilient,

rubbery coagulum, which comprisesremulsifyin'g an oil with a suificient quantity of an emulsifygum as emulsifying agent, adding to the emulsion a quantity of rubber-in'dispersed form not less in weight than the combined weights of the oil and gum, and coagulating the mixture by stirring in a small quantity of analdehyde with gentle warming.

9. A method of making a non-sticky, resilient, rubbery coagulum, which comprises making a stable emulsion of an oil with a water-soluble gum as emulsifying agent, adding to the emulsion a quantity of rubber in dispersed form not less in weight than the combined weights of the oil and gum, and coagulating the mixture by stirring in a quantity of 40% solution of formaldehyde equal in weight to about 2% V of the oil and solids in the mixture.

10. A non-sticky, resi1ient,- rubbery coagulurn' having the physical characteristics of a pure rubber coagulum, coagulated from a mixture of rubber in dispersed form and a substantial pro-'- portion of an oil in a stable emulsion with an emulsifying agent.

11 A non-sticky, resilient, rubbery coagulum having the physical characteristics of a pure rubber coagulum, coagulated from a mixture of rubber in dispersed form andfasubstantial proportion ofran oil in a stable emulsion with a water-soluble gum as emulsifying agent;

' 12. A non-sticky, resilient,.rubbery coagulum having "the physicalcharacteristics of a pure rubber in dispersed form and a'substantial proportion of a mineral oil in a stable emulsion with an emulsifying agent. I p 1' Y 13. A non-sticky, resilient, rubbery'coagulum having the physical characteristics of a pure rubber coagulum, coagulated from a mixture of rubber in dispersed'form and a substantial proportion of a mineral oil in a stable emulsion with,

a water-soluble gum as emulsifying agent.

14. A non-sticky, resilient, rubbery coagulum' having the physical characteristics of a pure" rubber coagulum, coagulatedfrom a mixture of fifty-parts by'weight of rubber in dispersed form and ten to twenty parts of mineral oil in a stable emulsion with forty to thirty parts of a water-soluble gum as emulsifying agent.

' FRANK O. WOODRUFF.

rubber coagulum, coagulated from a mixture of 

